The present invention relates to a DC-to-DC converter and more particularly to a DC-to-DC converter with an active power sink circuit.
FIG. 1 is a schematic diagram illustrating a conventional pulse width modulation (PWM) boost converter 100. When a main switch 101 is turned on, a full bridge rectifier 102 outputs a DC power source to a main inductor 103. Thus power is transferred from the DC power source to the main inductor 103 and stored in the main inductor 103. Meanwhile, a main diode 104 is reverse biased. Once when a main switch 101 is turned on, power stored in main inductor 103 is transferred from the main inductor 103 to a main capacitor 105. In theoretical, by assuming that the main capacitor 105 is large enough and the main switch 101 is turned on and off fast and periodically, electrical energy can be stored in the main inductor 103 and transferred form the main inductor 103 into the main capacitor 105 promptly. Thus the voltage across the main capacitor 105 can be maintained at a constant voltage without load variation effect.
However, during the switching operation of the main switch 101 in the boost converter, the reverse recovery current of the main diode 104 will cause the main switch 101 and the main diode 104 have a serious switching loss such that the switching frequency cannot be increased to reduce the size of the main inductor of the boost converter. Please refer to FIG. 2. FIG. 2 is schematic diagram illustrating another conventional pulse width modulation (PWM) boost converter 200. The converter 200 is provided to solve the above drawback. Basically, a branch circuit which has an auxiliary inductor 206 and an auxiliary switch 207 is added into the converter 200 in order to eliminate the reverse recovery current of the main diode 204. When the auxiliary switch 207 is turned on, the power of a main power source Vs is stored in the auxiliary inductor 206 and it causes the electrical energy of a parallel-connected capacitor 208 of the main switch 201 to be totally discharged and stored in the auxiliary inductor 206. Thus the main switch 201 can be turned on under the zero voltage switching condition. Furthermore, when the auxiliary switch 207 is turned off, the electrical energy of the auxiliary inductor 206 is discharged form the auxiliary inductor 206 to a capacitor 205 through a diode 209. Therefore, this technique can solve the switching loss of the main switch 101 and the main diode 104 shown in FIG. 1, but the switching loss of the auxiliary switch 207 is still existed (the auxiliary switch 207 is turned off), and the EMI and the RFI problem will be generated. Meanwhile, the PWM boost converter 200 further includes a full bridge rectifier 202 which is utilized to transferred an AC voltage into a DC voltage as a main power of the PWM boost converter 200. By utilizing the conduction of the main switch 201, the main inductor 203 can be charged by the main power.
For the above reasons, a need still exists in the art of designing and manufacturing DC/DC converter to provide an optimal configuration for low switching loss. The improved converter configuration will be described in this invention as below.
It is therefore an object of the present invention to propose a DC-to-DC converter with an active power sink circuit for eliminating switching loss of a main switch of the DC-to-DC converter by utilizing a resonant circuit to turn on the main switch under the near zero voltage switching condition and an active power sink circuit to cause a unidirectional switch to be turned off the near zero current switching condition.
It is therefore another object of the present invention to propose a clamped-mode DC-to-DC converter for generating a low voltage output and a high current output by utilizing a combined transformer-inductor device and a synchronous rectification circuit in order to minimize the primary switch loss, synchronous rectifier loss, transformer winding loss and transformer core loss.
According to an aspect of the present invention, the DC-to-DC converter includes a boost converter circuit, a resonant circuit, and an active power sink circuit. The boost converter circuit has a main switch for boosting a first DC voltage into a second DC voltage. The resonant circuit includes a unidirectional switch, a resonant capacitor, and a first winding of a transformer for causing the main switch to be controlled to exhibit near zero voltage switching. And, the active power sink circuit is magnetically coupled to the first winding of the transformer for draining energy in an inductance of the transformer off via magnetic induction between the active power sink circuit and the transformer, and causing the unidirectional switch to be controlled to exhibit near zero current switching.
Preferably, the boost converter circuit further includes a main inductor, a main diode, and a main capacitor in which when the main switch is turned on, the first DC voltage charges the main inductor and the main diode is turned off, and when the main switch is turned off, the main diode is turned on and the first DC voltage and a voltage across the main inductor charges the main capacitor to produce the second DC voltage.
Preferably, the main inductor, a first terminal of the main switch, and an anode end of the main diode are connected to a first node, and the other terminal of the main inductor is electrically connected to the first DC voltage.
Preferably, a cathode end of the main diode and a positive terminal of the main capacitor are electrically connected to a second node, and the second node is an output terminal of the second DC voltage.
Preferably, a second terminal of the main switch and a negative terminal of the main capacitor are electrically connected to a third node.
Preferably, the active power sink circuit is a push-pull DC-to-DC converter including a fist switch, a second switch, and a rectified circuit. The fist switch is electrically connected to a second winding of the transformer in series, and a series circuit of the fist switch and the second winding of the transformer electrically connected between the third node and the second node. The second switch is electrically connected to a third winding of the transformer in series, and a series circuit of the second switch and the third winding of the transformer electrically connected between the third node and the second node. And, the rectified circuit includes a secondary winding of the transformer having a first terminal, a second terminal, and a central terminal, a first diode having an anode end electrically connected to the first terminal of the secondary winding, a second diode having an anode end electrically connected to the second terminal of the secondary winding, and a cathode end electrically connected to cathode end of the first diode, and a first capacitor having a positive terminal electrically connected to a common cathode end of the first diode and the second diode, and a negative terminal electrically connected to the central terminal.
Preferably, the resonant circuit includes a third diode.
Preferably, the third diode having a cathode end is electrically connected to the first winding, and the unidirectional switch in series, and a series circuit of the third diode, the first winding, and the unidirectional switch is in parallel with the main switch and the resonant capacitor.
Preferably, the resonant circuit further includes a resonant inductor electrically connected to the first winding and the third diode in series.
Preferably, the transformer has a leakage inductance.
Preferably, the active power sink circuit is a full bridge DC-to-DC converter.
It is therefore another aspect of the present invention to propose a DC-to-DC converter including a boost converter circuit, a resonant circuit, and an active power sink circuit. The boost converter circuit has a main switch for boosting a first DC voltage into a second DC voltage. The resonant circuit includes a unidirectional switch, a resonant capacitor, a resonant inductor, and a first winding of a transformer for causing the main switch to be controlled to exhibit near zero voltage switching. And, the active power sink circuit is magnetically coupled to the first winding of the transformer for draining energy in an inductance of the transformer off via magnetic induction between the active power sink circuit and the transformer, and causing the unidirectional switch to be controlled to exhibit near zero current switching.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: